program declaration

    use, intrinsic :: iso_fortran_env, only: rk => real64
    implicit none

    integer :: i = 1                !! 单精度整型
    real(rk) :: x = 1.0_rk, xs(10)  !! 双精度浮点型标量 x 与 rank1-dimension10 数组 xs
    real(rk) :: y = 2.0_rk          !! 设置特定的浮点型精度

    xs = [real(rk) ::(i, i=1, 10)]  ! 数组赋值，隐式 do 循环

end program declaration
